>> joy reid back in just an hour at 10:00 a.m. don't go anywhere, many thanks to you both. that does it for "all in "for this evening and this week. i'm craig melvin. and i'm natalie morales. and this is "dateline." >> i'm craig melvin. >> and i'm natalie morales. >> and this is "dateline." oh, please, god, why? >> it's the case that stunned parents everywhere, the dad whose young son died in the car. >> apparently he forgot the child was in the car seat in the back, and went to work. >> i didn't mean to. >> i know you didn't. >> i think any parent could put themselves in that situation, full denial, that it wasn't happening. >> then came the jaw-dropping

news, police said it was murder. >> there was far more to this story that we were beginning to realize. this guy clearly was leading a double life. >> oh, my boy. >> could any parent ever do this on purpose? inside this landmark case. >> there were a whole lot of secrets about to be revealed. >> yes, ma'am. >> for all the picture perfect world, was shattered, one hot georgia day when their toddler cooper was left in a car for seven hours and died from overheating. was this a horrific mistake, or murder? here's andrea canning with "unimaginable." >> reporter: you're watching as a police cruiser races to an atlanta parking lot. a call for help has come over the radio. "child not breathing." he'd been found in the back seat of a hot car.

every year an average of 37 children die from heatstroke after being forgotten or left behind in cars in the heat of the sun. and parents pay the ultimate price for lives that are busy, distracted, sometimes overwhelming. police weren't able to save 22-month-old cooper harris a few -- in 2014, and his death in a hot car made headlines nationwide. >> new details in a tragic case we've been following, the death of a georgia toddler. >> reporter: but there was something different about cooper's story. something darker. because cooper's dad, ross harris, ended up being charged with a crime. accused not of forgetting cooper but of murdering him. and his murder weapon of choice, prosecutors said, was a hot car. but even if you've seen the headlines, there's a lot more to this story you may not know.

tonight we'll take you to the scene, show you surveillance footage from that day and give you an in-depth look at the evidence. >> it sent chills down our spines knowing we were in the head of a murderer. >> reporter: we'll also talk to insiders who have never spoken out before. they say ross harris was not a killer but a doting dad. was he a proud dad? >> so proud. >> he loved that boy. >> reporter: a father who ended up on trial for an unimaginable crime. >> the entire case was a house of cards. >> reporter: and just like the people around him, you can decide, is this the face of a dad who just made the worst mistake of his life, or a murderer? >> oh, my god. what have i done? ♪ >> reporter: ross harris grew up in tuscaloosa, alabama, and that's where his close friend,

billy kirkpatrick, met him. you called him a massive dork? >> massive dork, yes. >> reporter: why did you call him that? >> because he's a massive dork. >> reporter: billy says ross was a lot of fun to be around. he remembers one beach holiday in particular. >> ross took his guitar and, like, walked up to people on the beach and started conversations because that's who he is. >> but ross seemed to settle down when he met his wife, leanna. she encouraged him to get his college degree. his cousin katie, who quickly became leanna's best friend too, says leanna made ross want to be a better man. >> we've said that without leanna, ross would've probably been a lost little puppy. >> reporter: after six years of marriage, they moved to atlanta when ross was offered a job as a web developer at home depot. cooper was born a few months later. what was it like for you, the first time that you -- that you saw cooper? >> oh, man, he was so beautiful, just blonde hair, blue eyes.

just tiny little perfection. >> i just had this vision of, you know, ross and cooper on the couch and ross is just goofing around with him and get on the floor with him. and it's hilarious. >> any extra thing that cooper could do, any milestone that he hit, he would share it with everyone. one of the conversations i had with ross, he said that it was so cool that cooper knew his name. and he said, and he loves to yell it at me. so instead of saying dad. he would just go, ross! and he would yell "ross" at him all the time. >> reporter: it was ross who took cooper to day care most mornings. and that was where leanna expected to pick him up on june 18th, 2014. here she is arriving at the day care. >> she got to the day care and cooper wasn't there. >> reporter: leanna called ross to see if there had been a mix-up, but he didn't pick up. and then she had a worrying thought -- maybe ross had accidentally left cooper at home.

>> she texted her neighbor and asked her to just go look. she has a key to her apartment. just go look. see if he's there. and she was like, maybe the house will just be torn up. it had be a little toddler tornado when she gets there, but he'll be there. obviously, he wasn't. >> reporter: leanna rushed over to ross's office to see if cooper was there. it was at home depot that a police officer tracked her down. their conversation was recorded as he gave her the worst possible news. >> there ain't no easy way to tell you this. your child is deceased. i'm very sorry to have to tell you that. >> where is my husband? >> your husband is up at our headquarters right now. >> reporter: the officer explained ross had never taken cooper to day care that day. that he'd done the unthinkable, and left cooper in his car for seven hours in the georgia heat. >> has he ever done anything like that, forgetting about -- >> no.

>> do you know what might have made him forget about it? >> no. >> i think any parent could put themselves in that situation with their own child. and it's so hard to fathom being in a place like that. >> i think she was in full denial, like, that it wasn't happening. it was a nightmare, is what she said. i'm going to wake up and it will be fine. this didn't happen. >> reporter: leanna was taken to the cobb county police headquarters. ross was already there in an interview room, telling detectives what had happened. but to them, something about ross harris and his story wasn't adding up. >> what really happened that morning? was it a tragic accident or something far more sinister? coming up -- >> oh, please, god, why? >> questions about a father's story. >> the antennas went up on the detectives when they heard that. >> when "dateline" continues.

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oh-- andrea canning: ross harris sat alone in the place they call the box, an interview room at the cobb county police department. ross harris sat alone in the place they call the box, an interview room at the cobb county police department. >> oh, please, god, why? >> reporter: he could barely keep still as he waited for detectives to question him about the death of his son cooper. he had a horrible story to tell. >> ross, just kind of run me

through your morning today. >> reporter: prosecutor chuck boring was brought into the investigation early on. >> i think the main goal in a case like this is to get a timeline of the events. >> reporter: ross told detectives the morning had begun like many others. leanna set off to work early. ross set out to take cooper to daycare and decided to stop for breakfast at chick-fil-a near his office. >> and me and him do that at chick-fil-a in vinings approximately two or three times a month together. >> reporter: after they ate, ross said he strapped cooper into his car seat. >> i gave him a kiss. he gave me a kiss. what i do every time. it's my routine. and just today was just like, careless. i got in my car, and instead of going from here to here, i went straight to work. >> reporter: ross told police he'd simply forgotten to take cooper to day care. >> i went to work. as if he wasn't even in the back. and i probably didn't even hear him because he falls asleep

really easily when you drive the car. and that was it. >> reporter: he said he didn't realize what he'd done until hours later when he got in his car after work and started driving. >> i caught a glimpse of him in my -- when i looked to my right to change lanes. >> reporter: ross said he went flying into the closest parking lot and pulled a lifeless cooper out of his car. a bystander called 911. >> there's a baby on the ground. >> reporter: dash cam video from a police cruiser captured ross at the scene minutes later, pacing, hands on his head. >> i need your i.d. where's it at? >> reporter: it also captured audio of ross exploding in anger at police. >> shut the [ bleep ] up. hold on. my son died. all right. all right. all right. all right. >> you watch your [ bleep ] mouth. >> reporter: they cuffed him and put him in a patrol car to cool off. and this was the moment when police started wondering about the way ross was behaving. he cried out one moment.

>> oh, my god. what have i done? >> reporter: the next moment he seemed calm. >> we're going to sit here and talk a little bit. >> reporter: at the police station, detectives who interviewed ross thought his demeanor seemed a bit strange. they noticed he'd never shed a tear in front of them. instead he was casual as they searched his pockets. >> i'm the lead guitar player at stonebridge church in the square. >> okay, yeah. >> reporter: even jokey -- >> and english is your primary language? >> it is. >> okay. >> if not, i'm doing really good. >> reporter: prosecutor jesse evans. >> you look at it and say whatever the reaction is that you're supposed to have, that ain't it. >> reporter: but what really got detectives' attention was how much ross seemed to know about children dying in hot cars. >> the worst fear for me is to leave my son in a hot car. and then, just recently, there was a vet on -- on the internet who said even if you've got your windows rolled down and regardless, you know, i'm going to show you how hot it can get in the car.

>> the antennas went up on the detectives when they heard that. >> reporter: detectives weren't in the room when ross was finally reunited with leanna, but the cameras rolled. and ross showed a completely different emotion to his wife. >> you know i didn't mean to. >> i know you didn't, baby. i know you didn't. i know that. >> i didn't mean to. >> i know you didn't. >> i think my life is over. >> it's not over, baby. it's not over. >> reporter: ross pulled himself together and told leanna his story just like he'd told the police. >> i turned out of chick-fil-a, and i just went to work. like -- like it was nothing. he wasn't making a sound. you know, i think he fell asleep. >> reporter: he had some comfort for leanna, too. >> at least i know that he's in heaven right now. >> i know he is. >> i know he is. >> he's playing with all the trucks in the world. >> oh, my boy.

>> reporter: but it was something else ross told leanna that really got the investigators' attention. >> i was up and down, dreading he was going to look terrible. >> he said it while he was talking to leanna that, you know, he was dreading how cooper was going to look when he got him out. >> reporter: almost like -- >> he knew what was there. exactly. he knew what was going to be found. >> reporter: they were also struck by how calm leanna seemed to be. and by this surprising question. >> did you say too much? >> reporter: detectives wondered what she meant. they came back into the room and told ross he wasn't going home. >> he's going to jail. he's being charged. >> reporter: investigators thought they had enough to prove ross had been negligent by leaving his son in the car. >> his negligence caused the death of your son. >> reporter: and their investigation was just beginning. later that night, when katie reached leanna on the phone, she told her she'd been sitting outside her home on the sidewalk. >> and she's told me that, you know, as long as she sat outside, she could pretend like

this wasn't happening. because once she goes inside, you know, there's an empty bedroom where cooper's supposed to be. >> reporter: an empty crib? >> there's his toys, his pictures. it's not real if she doesn't go inside. >> reporter: katie says leanna was numb without her child and her husband. did she go through that emotion at any point, i'm angry at you? how could you do this? >> i don't know that she was ever angry at him. >> reporter: because you go through that scenario as a parent, what if my spouse did this? would i be able to understand? >> but she's such a composed woman. and her faith, i don't think, would let her be angry at him for something that he did not do intentionally. >> reporter: as cooper's family began to grieve, detectives started building their case against ross harris. and what they found convinced them this was no simple case of negligence. they believed this was premeditated murder.

coming up -- >> did he lie? >> he absolutely lied. >> there were a whole lot of secrets to be revealed? >> yes, ma'am. >> when "dateline" continues.

after his son, cooper, died from being left in a hot car, ross harris was brought in for questioning. even though harris was apologetic to his wife, >> after his son cooper died from being left in a hot car, ross harris was brought in for questioning. even though harris was apologetic to his wife, authorities were not convinced. they charged him in the death of

his son. the father may have been negligent in forgetting cooper was in the car, but were his actions intentional? here again is andrea canning. the day after cooper's death, ross harris sat in the cobb county jail. his family and friends were in shock. billy was a pallbearer at cooper's funeral. >> you have to carry that -- that little casket. you know? >> reporter: katie says the family grieved in full view of the media. >> i felt like it was a circus and we were the monkeys. everybody was watching us. >> reporter: police were watching, too. prosecutor susan treadway. >> we have to review all of the evidence, we have to see where

it leads us. >> reporter: investigators pulled surveillance video from the chick-fil-a restaurant where ross said he took cooper for breakfast. there they were, father and son. >> nothing really seems out of the ordinary. i mean, this looks like a father and son grabbing breakfast. it doesn't look like a child killer waiting to carry out his crime. >> i would say completely to the contrary. i looked at the video, and when i first saw it and i thought it seemed very out of the ordinary. in particular, the way that he was introducing cooper to some of the workers there. and how they eventually described it to us as being almost like he was putting on a show, almost like he was going out of his way to do that. >> reporter: but maybe more interesting, prosecutor jesse evans says, was what the video showed about cooper. >> cooper's wide awake. didn't appear to be sleepy or anything like that. >> reporter: ross had told detectives cooper was most likely asleep in the car, and that's why he'd forgotten about him. >> but detectives were skeptical. the entire drive from the restaurants to ross's office was only about half a mile.

and there was something else investigators found interesting about ross's route that day. it's how quickly he would have forgotten cooper if it happened the way he said. we decided to retrace ross's route that day. we're making a right out of the chick-fil-a parking lot and we have to cross a lane of traffic just as ross did to get to this u-turn right here. he made this u-turn very quickly and then headed toward this intersection up here. and this is a critical intersection coming up. it was here ross had to make a decision. going left would have taken him to cooper's daycare. going straight on would have taken him to work. he went straight on. that means he forgot cooper was in the car within two minutes of strapping him into his car seat and giving him a kiss. >> it does seem remarkable that we can forget a child in a car very quickly. >> reporter: dr. david diamond is a neuroscientist at the university of south florida. for a decade he has studied hundreds of cases of children who die in hot cars. >> in a recent case i was involved in in australia, a

mother drove one block, a 30-second drive, and in a matter of that brief time forgot that her child was in the car. >> reporter: what we're talking about here, there is actually a name for this. >> this is referred to as forgotten baby syndrome, which actually describes a phenomenon in which normal, attentive and loving parents, for reasons we don't fully understand, lose awareness that their child is in a car. >> reporter: diamond says it can happen to anyone. distraction and exhaustion often play a role. he adds, once the child is forgotten, the brain plays a dangerous trick. >> what's remarkable about these cases is that these parents actually create sort of an artificial memory that the children are actually at day care and that they are safe. >> reporter: but in this case, investigators were increasingly convinced that cooper's death had nothing to do with a slip of the mind. there's been a lot made of how could you forget something that quickly. now, i don't know what was going

through this man's mind, but i do know that i have five children and i forget things in an instant. it just happens. is it fair to say, oh, he wouldn't be able to forget something so fast? >> this is something that if you look at it alone, can somebody forget something that fast? is it possible? yes. but then you look at the location of the car seat and all of the other factors together and that showed us that he could not have. >> reporter: investigators noted that cooper's car seat was just inches from the driver's seat. and when they looked at surveillance video from ross's work parking lot, they saw this, video of ross backing up before he parked. they were sure ross must have seen cooper when he backed up. we wanted to see for ourselves. we're in the same kind of car ross harris was driving. we've placed the same model of car seat in the same spot cooper was sitting. if i turn around, i can definitely see it. if i use my mirrors to back up, i can't.

and there was another detail the surveillance video from home depot revealed. ross had gone to lunch with some friends. there he is getting picked up. but look here, nearly an hour later, there he is again getting dropped off at his car. he opens the driver's door and throws a box of light bulbs onto the front seat. ross never told detectives about going back to his car in the middle of the day. did he lie about going to the car or did he just not disclose that he had gone to the car? >> i think when you look at it in totality, he absolutely lied about it. >> reporter: investigators were sure ross was hiding something. they believed there was no way he could have opened that door and missed his son in the back seat of the car. did you consider the possibility that maybe he really did just throw the light bulbs in there and didn't see cooper? >> absolutely, but when you look at everything else in the case, absolutely not. >> reporter: and that "everything else" included what

investigators uncovered on ross's cell phone. there were a whole lot of secrets to be revealed? >> yes, ma'am. coming up -- >> did you engage in sexual acts with him? >> yes, on three different occasions. >> this guy clearly was leading a double life. >> when "dateline" continues. il chronic, widespread pain. fibromyalgia may be invisible to others, but my pain is real. fibromyalgia is thought to be caused by overactive nerves. lyrica is believed to calm these nerves. i'm glad my doctor prescribed lyrica. for some, lyrica delivers effective relief for moderate to even severe fibromyalgia pain. and improves function. lyrica may cause serious allergic reactions, suicidal thoughts or actions. tell your doctor right away if you have these, new or worse depression, unusual changes in mood or behavior, swelling, trouble breathing, rash, hives, blisters, muscle pain with fever, tired feeling, or blurry vision. common side effects: dizziness, sleepiness, weight gain, swelling of hands, legs and feet. don't drink alcohol while taking lyrica.

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>> the mayor in hrge ravaged san juan said the trump administration is killing us with inefficiency. the comments come as the acting homeland security secretary visited puerto rico and said the situation is not satisfactory, but she did say she's proud of the work the u.s. government is doing. another trump official is out. tom price resigning over uproar over his use of private jets and military planes. more news in one hour. i'm craig melvin. investigators probing the hot car death of cooper harris

discovered video evidence they say welcome back to "dateline." i'm krase melvin. investigate sors probing the har car death of cooper harris say they discovered it proof his father would have known she was still in the car. secrets were about to be revealed, that could provide a glimpse into a possible motive for murder. here again is andrea canning. police were suspicious of ross harris from the moment they met him on that first terrible day. but their next discovery would turn this strange case into an explosive one. police seized his phone and computers. and that's when they found the photos and texts. >> this guy clearly was leading a double life. >> reporter: investigators found a sordid stash of sexually explicit online chats and texts between ross and a number of women, one as young as 15. and what's more, some of the

sexual chats happened on the very day cooper died. he was communicating with a woman -- >> right. >> reporter: -- ten minutes before he left with cooper? >> right. we were able to determine that he had been messaging at least six different women throughout that day, sending pictures of himself, asking for photographs. >> reporter: prosecutors believed ross harris was in the grip of an escalating obsession with sex. and they came to an awful conclusion. that ross wanted so badly to be rid of the constraints of family and fatherhood, he decided to kill his own child. does being a creep with women make him a child killer? >> absolutely not. in this case, though, it showed us the extent to which he was living the other life. it showed us how it had overtaken in his life what was important to him. >> reporter: so they threw the book at him. ross was indicted for malice murder, the first person ever to be accused of using a hot car to intentionally kill a child.

the case became a media sensation with more revelations. investigators said ross had done internet research on hot car death and even visited an online forum for people interested in living a child-free life. a monstrous portrait was emerging. but even after weighing all the allegations, ross's friends were still convinced he never meant to hurt cooper. did you ever hear ross get frustrated with cooper? >> no. >> reporter: treat him like he was a burden at times? >> no. >> reporter: because you know there are times when kids can get on our nerves. >> mm-hmm. no, no. there are times when you definitely need a break. okay? but he loved that boy. >> reporter: ross harris's family enlisted the help of defense attorney maddox kilgore and his team. >> the entire case was a house of cards. we felt that, despite public sentiment, and despite the

bravado of the state and the charges, we felt extremely confident that that house of cards was going to collapse in trial. >> reporter: in october, 2016, more than two years after the death of his son, ross harris went on trial for murder. >> death. deception. and a double life. >> reporter: chuck boring, the lead prosecutor, told the jury why ross's story had never added up. that chick-fil-a video showed cooper wide awake. that drive that was too short to forget a toddler. the car seat was just inches behind ross. and at ross's office, there was a photo of cooper and a gift from cooper. he even sent a text to leanna in the afternoon about cooper. when you getting my buddy, it said. none of that jogged his memory? >> there was just cue after cue after cue that if he had actually forgotten would have triggered something. >> reporter: and then the

prosecution showed what it believed was powerful evidence that ross had to have known that cooper was still in the backseat. that video of ross returning to the car. why would ross harris return to the scene of the crime? >> we know, first of all, doing this job enough, people do return to their scene of the crime. once he went into the car, he realized either this child was still alive or this child was dead and he couldn't take what he had done and he threw the light bulbs. >> reporter: and prosecutors dissected ross's behavior later that day. witnesses at the scene testified his reactions were off. >> did he ever ask to be with the child or ask to hold the child or anything like that? >> no, sir, not that i recollect. >> reporter: prosecutors pointed out that when ross got into the patrol car he complained about, of all things, the heat in the back seat. >> feels like i'm not getting any air back here. >> reporter: and while jurors heard that ross seemed disconnected from his son's death, they also heard he was obsessed with the sexual

contacts he'd made outside his marriage. a parade of women took the stand. a woman ross had said he was in love with. another women he met at his home. >> we had sex. >> reporter: and a prostitute. >> did you actually engage in sexual acts with him back in may of -- >> yes, on three different occasions. >> reporter: this witness is one of the six women ross was communicating with the day he says he forgot about cooper. >> and at 5:46 a.m., within 17 seconds of your messages, did he respond? >> he did. >> reporter: did you have to consider the fact that maybe all these women were causing a distraction for ross, which then led to what happened versus that the women were actually a motive? >> oh, absolutely. but when you look closely at the content of the messages and what's going back and forth specifically you're trying to prove to a jury that this person had the intent in his mind to kill his child. you have to get to know that person. you have to get to know what they're made of.

>> reporter: and prosecutors say one message in particular said it all. just minutes before ross strapped cooper into his car seat for the last time, he messaged a woman on an anonymous app called whisper. he typed this. "i love my son and all, but we both need escapes." >> honestly, it sent chills down our spines knowing we were in the head of a murderer. >> reporter: nonsense, according to the defense. >> if he is in the throes of committing a heinous murder, is he really going to announce that by texting it through this application right in the middle of doing it? >> reporter: ross's defense team says the entire case against him was outrageous, built on evidence that was twisted by prosecutors to make him look like a killer. they say that message about escape, for instance, was about hanging out with friends, not killing his son. >> if you take that one message in isolation, you can make it mean all kinds of things.

>> reporter: another case in point, that child-free website ross supposedly visited? he actually found it repulsive. >> the link was sent to him by a friend in jest. ross goes to the link, looks at it, and he responded, "grossness." >> reporter: and the defense says there was more misinformation released early on, like that story about ross researching hot car deaths. ross had clicked on one video posted on a popular website about pets and hot cars, but the defense said that was hardly research. a computer expert testified ross never actively searched for information on hot car death. >> i didn't see him searching for anything at any point in time that would have been how to kill a child in the car or hot car deaths or anything like that. >> reporter: as far as his return to the car that day? the defense says ross had no idea his son was in the back seat.

never even glanced inside as he tossed the light bulbs onto the front seat. look at this angle of the video. >> the proof was his head never got below the roof of that car. the proof showed that he was turning in the other direction. >> reporter: but what about those reminders during the day? shouldn't one of those have triggered his mind to say, wait. cooper. where's cooper? >> i think that's a fair question to ask. if ross had forgotten that he had a son, seeing a picture of cooper would have reminded him that he had a son. he didn't forget he had a son. once ross slipped into his work day, he had every reason to believe that cooper was at the daycare. >> reporter: as for those witnesses who said ross seemed detached, they didn't know him, the defense argued. so they called people who did, like his friend billy. >> in my opinion, he was just incredibly loving and doting. >> reporter: a colleague from home depot. >> when cooper was born it's all

he would talk about. >> reporter: even prosecution witnesses wound up vouching for ross as a good dad. a teacher from cooper's day care. >> he would just spend quality time with him interacting with him doing the activities. >> reporter: and some of those women who testified for the prosecution about sexting with ross? even they agreed he seemed to love his kid. >> what would he say about his son? >> that he was great, and that he loved his son. >> he just talked about how much he loved him and how he would never do anything to hurt him and that kind of thing. >> reporter: but the woman who should have known ross harris best was about to take the stand. she had something to say about the man who betrayed her, and left her son to die. and it may be the last thing you'd expect to hear. coming up -- >> cooper was the sweetest little boy. >> heartache laid bare. cooper's mom tells her story. >> i just kind of went into a panic.

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go to lendingtree.com right now. andrea canning: leanna harris had lost so much-- her child and her life as she had known it. leanna harris had lost so much. her child and her life as she had known it. by the time ross went on trial, leanna had heard all the revelations she could stand, and she had divorced him. if anyone had a reason to hate ross, to be angry at ross, to not get up on that witness stand for ross, it's her. >> right. >> reporter: but yet she did.

>> because she believes 100% that it was not intentional. >> reporter: so there she was in court, not condemning ross, but defending him. >> tell these folks a little about cooper. >> cooper was the sweetest little boy. he had so much life in him. he was everything to me. >> reporter: and everything to ross, too, she testified, as the jury watched family videos of father and son. >> what are we looking at there, leanna? >> that's them in our bed. and that's just kind of a little game that they would play. >> reporter: leanna said ross was the kind of dad who always played at the park. >> you do it, go. ♪ >> reporter: and made goofy videos of his son at snack time. you want it?

>> yeah. >> did ross love his little boy? >> yes, he did. very much. >> did you ever see ross express anger or hatred or malice toward his son ever? >> no, never. >> reporter: then came that terrible day. the courtroom was silent as leanna described arriving at cooper's daycare and being told he wasn't there. >> she said, he didn't come today. and i just kind of went into a panic. i didn't know what to do. i was just -- it didn't make sense. cooper was supposed to be at daycare. i was supposed to be the one to pick him up. it didn't make sense. the only thing that made sense to me, based on everything that i knew that day, ross must have left him in the car.

>> reporter: it made sense because she knew ross so well. he could be forgetful. and when she saw the video of him with police, she recognized that ross, too. >> this morning we woke up -- >> reporter: the overly-social guy just chatting away. >> he just would talk to everybody, very outgoing, very vocal. he didn't -- he never met a stranger. >> reporter: but leanna also told the jury how ross looked when she first saw him at the police station. she says he was in terrible pain. >> it was very difficult to see him like that. >> reporter: this was the true face of ross's grief and guilt, the defense said. and leanna explained to the jury why she asked ross that question that made investigators so suspicious. >> did you say too much?

>> i couldn't understand what was happening. i didn't understand why he was being charged. and the only thing that i -- that i could think in my head was what did you say? and so those words came out. >> reporter: as for that prosecution theory that ross had wanted to escape his family for his secret life, leanna said it wasn't true. she'd known for years that ross had a problem. >> i came home from work one day, and he told me that he had a problem with pornography. two years after that probably, i found a message on his phone that i guess you would describe it as sexting. >> reporter: she said they worked hard to save the marriage, and if ross had wanted out, all he had to do was ask. >> i just very bluntly one night said, do you want a divorce? i mean, if you want a divorce, you can have it.

i will give it to you, if that's what you want. and i believe his answer back to me was, that's the last thing i want. >> reporter: prosecutors told us there was no evidence leanna knew what her husband was supposedly planning. and when they cross-examined her, they suggested she didn't know her husband at all. >> you'd agree there's a whole part of his life that you had no clue about? >> i would agree that i did not know the depth. >> have you read the text messages that he sent to these other women? >> no. i have no -- i have no reason to have read them. >> okay. so if he's saying foul things to a 15-year-old girl, you wouldn't think that that was something different than the way he portrayed himself to you? >> i think it's horrible. >> reporter: the prosecutor pointed out that ross lied to her all the time. one example -- >> did you know that was the afternoon he actually called a prostitute and went to have sex with her instead of being at home with you and cooper?

>> i didn't know that. >> reporter: humiliating as it was, she stuck it out for nearly two days of testimony. >> that woman had every reason in the world to hate ross harris. and despite all of that, despite all of that, she was willing to come testify for him because she knew what the truth was. >> reporter: and then, in his final question to leanna, ross's attorney wanted to make something clear. leanna was there for one reason only -- she believed that what happened to cooper was a mistake, not a crime. and now she was ready to walk away. >> how do you feel about your ex-husband? >> he ruined my life. he destroyed my life. i'm humiliated. i may never trust anybody again the way that i did. if i never see him again after this day, that's fine. >> nothing further, judge. coming up --

>> ross harris is an innocent man. >> the jury has its verdict. when "dateline" continues. parts a and b guess what? you could apply for a medicare supplement insurance plan whenever you want. no enrollment window. no waiting to apply. that means now may be a great time to shop for an aarp medicare supplement insurance plan, insured by unitedhealthcare insurance company. medicare doesn't cover everything. and like all standardized medicare supplement insurance plans, these help cover some of what medicare doesn't pay. so don't wait. call now to request your free decision guide. it could help you find the aarp medicare supplement plan that works for you. these types of plans have no networks, so you get to choose any doctor who accepts medicare patients. rates are competitive, and they're the only plans of their kind endorsed by aarp. remember - these plans let you apply all year round.

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welcome back. leanna harris testified that her husband, ross, did not mean to kill their toddler, cooper. >> welcome back. leanna harris testified that her husband ross did not mean to kill their toddler cooper. but the prosecution had presented a compelling case pointing to his guilt.

what will the jury decide? here with the conclusion to our story is andrea canning. ross harris, the man whose ex-wife says never met a stranger, was about to have his future decided by 12 of them. how were you all feeling as the jury went out to deliberate? >> i didn't think there was any chance of them coming back with guilty on anything that had to do with cooper. >> reporter: ross's cousin katie said nothing she had seen at trial had swayed her belief in ross's innocence. >> you could hold a gun to my head and tell me that i had to say that ross hurt cooper on purpose, and it will never come out of my mouth. will never come out of my mouth. >> reporter: ross's best friend billy was equally confident. >> the prosecution did not do well at all. they did not prove motive. i mean, they didn't get close to it. in fact, i feel like their witnesses could have been defense witnesses. >> reporter: the jury took its time to deliberate the charges. not only multiple counts of child cruelty and murder.

ross also faced charges related to exchanging sexually explicit images with a minor. one day passed, then two, then on the fourth day word came. a verdict. >> we, the jury, find as follows, count one, malice murder. as to count one we find the defendant guilty. >> reporter: guilty on all counts. i'm sure you'll never forget that moment. >> it's ludicrous. it's insanity. >> reporter: what would you say to the jury? >> i'm disappointed. i don't feel like they did their job. >> reporter: we wanted to know how the jury reached its decision. none of the jurors would speak to us on camera, but one did tell us they paid close attention to that video that shows ross harris returning to his car at lunch time. in fact, the jury wanted to re-examine the video during deliberations. the juror also told us that in his heart of hearts he believes ross harris meant to kill his son.

the prosecution says the jury got it completely right. but hearing the word "guilty" was no cause for celebration. >> what i wanted to hear most is, you know, we can bring cooper back. you can't get that from it though. >> reporter: three weeks later, a judge sentenced ross harris to life in prison. >> sentence of the court is life to serve in confinement without parole. >> reporter: his defense team has already filed an appeal, arguing among other things that the judge never should have allowed all that testimony about sex into the murder trial. and the defense says inaccurate information released early on about ross's computer searches made it impossible for him to get a fair trial. >> our personal belief, not lawyer talk, our personal belief and knowing ross and knowing this case better than anybody in the world, ross harris is an innocent man. >> reporter: are you going to keep fighting? >> this case is far from over. >> reporter: having seen the

appeal, vic reynolds, the top prosecutor in cobb county believes it won't change the outcome. >> i have complete confidence in the jury's verdict, complete confidence in the evidence that was presented, and i believe when the day comes, this verdict will, in fact, be affirmed. >> reporter: but ross harris's supporters say there is another tragedy in all this. they believe his conviction will make things worse for parents who make similar, terrible mistakes. >> this sets the precedent that anyone that does this is a monster. and that's just not the case. this really can happen to anyone. >> reporter: cooper's family may never stop grieving for the little boy who had just learned to say his dad's name, loved his trucks and loved to smile. what does leanna want cooper's legacy to be? >> that he was loved. he was very loved by everyone that knew him, especially his parents.

that's all for this edition of "dateline." i'm craig melvin. thanks for watching. and i'm natalie morales. and this is "dateline." i'm greg melvin. >> i'm natalie morales. >> and this is date line. >> she's dead, she's dead! and i was so confused. i was like what's going on? what happened? >> a small texas town, two super close friends and a summer night in the park. >> they have this lookout and you could see